ShltAbyss
Member
- Location
- MB, Canada
Designing a PV system, Max DC voltage calculated using (CEC) 64-202(2) is 614V,
is 600Vdc equipment permitted?
is 600Vdc equipment permitted?
Equipment Voltage rating
- Thread starter ShltAbyss
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electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Although I cant reliably say much of anything about the CEC, I would say if you calculate voltage by the prescribed routine, then that is what it is. The NEC has 690.7 which states how to calculate system voltage and it specifically says that shall be used to determine the voltage rating of equipment.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Electrical Engineer - Photovoltaic Systems
In a word, no. That said, I don't know what (CEC) 64-202(2) is. I use ASHRAE minimum temperatures with the manufacturer published Voc and temperature correction factors to calculate maximum string voltage. 600V is a hard stop.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
But only for Residential in the US, yes?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
2014 restricts PV circuits to 600 volts "in one and two family dwellings."
Also, IIRC 2017 allows calculation of max voltage using software that takes into account irradiance. That doesnt mean you can go over 600, but it does mean with that method you would get higher voltage than you would going solely off the temperature.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Electrical Engineer - Photovoltaic Systems
No, that's for any inverter that publishes a 600V maximum DC voltage. Some inverters will record the maximum DC voltage they have seen and void the warranty if it is greater than 600V.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Electrical Engineer - Photovoltaic Systems
But not by much. Voltage doesn't change much with irradiance.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Often enough for an extra string. I'll take it.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Electrical Engineer - Photovoltaic Systems
If the voltage correction is higher considering irradiance and you have a hard stop at 600V, that could cause you to lose a module in a string. I don't see how changing the way you calculate string voltage could result in getting an extra string in parallel, though; can you elaborate? Show me the numbers.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
2017 allows PE's on systems of 100 KW or larger to use modeling software to establish voltage ratings (and current too!). The standard method the just employs temperature correction is very conservative and not realistic. Sure irradiance doesnt effect VOC "much", but it only takes a few percent on 1kv strings until you are at another string. Sandia National Laboratories' photovoltaic array performance model is one such model, and I believe that is essentially what is incorporated into most common PV software programs like PVsyst and helioscope. I have never used these programs nor do I have any results to relay. I can only speak from many field measurements where the VOC is always way below the temperature corrected nameplate value, and I assume this is exactly what the software is modeling.
The larger the system is, the bigger deal this is. Take a 200 KW system and say we have 18 modules per string instead of 17. That is 37 strings instead of 39. Not that big a deal. But consider a 2.5 MW with 8000 panels with that 18th module. That saves 25 strings. The guy pulling those 600 foot runs of #8 PV wire in the mud and rain for 3 weeks (that was me last late fall) would probably make you an apple pie for every string you were able to get rid of
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Electrical Engineer - Photovoltaic Systems
2017 allows PE's on systems of 100 KW or larger to use modeling software to establish voltage ratings (and current too!). The standard method the just employs temperature correction is very conservative and not realistic. Sure irradiance doesnt effect VOC "much", but it only takes a few percent on 1kv strings until you are at another string. Sandia National Laboratories' photovoltaic array performance model is one such model, and I believe that is essentially what is incorporated into most common PV software programs like PVsyst and helioscope. I have never used these programs nor do I have any results to relay. I can only speak from many field measurements where the VOC is always way below the temperature corrected nameplate value, and I assume this is exactly what the software is modeling.
The larger the system is, the bigger deal this is. Take a 200 KW system and say we have 18 modules per string instead of 17. That is 37 strings instead of 39. Not that big a deal. But consider a 2.5 MW with 8000 panels with that 18th module. That saves 25 strings. The guy pulling those 600 foot runs of #8 PV wire in the mud and rain for 3 weeks (that was me last late fall) would probably make you an apple pie for every string you were able to get rid of
OK, but doesn't taking irradiance into account increase Voc?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
The guy pulling those 600 foot runs of #8 PV wire in the mud and rain for 3 weeks (that was me last late fall) would probably make you an apple pie for every string you were able to get rid of
One might think he would be happy to be getting the extra pay for the extra work.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
No, lowest temps will occur early in the morning, and that is when irradiance will be lowest.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Not if he bid on the job per watt instead of per hour.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
In general I really hate to see waste, even if it benefits me. It just drives me crazy. I also want solar to thrive and do well, so I hate to see inefficiency and waste. Plus, pulling wire in the mud and rain for three weeks is backbreaking and not very fun.
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